.mdbook-icon {
  height: 1em;
  vertical-align: middle;
}

h1 .mdbook-icon {
  height: 2em;
  vertical-align: middle;
}

h2 .mdbook-icon {
  height: 1.5em;
  vertical-align: middle;
}

h3 .mdbook-icon {
  height: 1.17em;
  vertical-align: middle;
}